Shear-thickening fluids or “dilatant” materials have the unusual property of a viscosity that increases with the rate of shear strain within the fluid. Several structures have been offered that attempt to exploit this property by incorporating shear-thickening fluids into fabrics or pads. In some prior approaches, this is accomplished by encapsulating a wet phase shear-thickening fluid into sealed bags, with syntactic glass beads for weight reduction. Other approaches incorporate the shear-thickening fluid into solid phase elastomers. The structures stiffen on impact thereby spreading the impact force over a relatively wide area, with more stiffness at higher speeds for protection and less at lower speeds for movement and comfort. The shear-thickening material is therefore used to improve pad dynamics.
The degree of dynamic variation in pad properties can be modified in these prior approaches according to the amount of dilatant, its formulation (e.g. amount of silicone beads by volume, bead shape, and bead size). A direct result of tuning the dynamic response of a pad is the impact speed at which the material starts to harden, and the resultant load spreading in the pad. Where low weight is desirable, products incorporating shear-thickening fluids are often rated by the amount of shear-thickening reaction available, divided by the area weight. Examples where weight is critical are helmet pads, body armor, gloves, and safety equipment.
In view of the foregoing, it would be an advancement in the art to provide a pad incorporating a shear-thickening fluid that provides both comfort and impact resistance as well as being lightweight.